1) Field of the Invention
The present invention relates to a gap adjustment apparatus and a gap adjustment method, and more particularly, to a gap adjustment apparatus and a gap adjustment method suitable for adjusting a gap between a wafer and a mask (which are both used in X-ray lithography and electron beam exposure).
2) Description of the Related Art
In X-ray lithography and electron beam exposure, a mask is usually disposed in a position above a wafer (which will later be exposed) with a small gap formed between the wafer and the mask. In this manner, the surface of the wafer can be subjected to an exposure treatment by passing light through the mask. However, in order to improve the resolution and alignment precision, it is extremely important to precisely control the gap between the wafer and the mask. In particular, if such a gap is too large, a half-shadow problem will occur, resulting in reduced resolution as well as reduced alignment precision.
As a method for measuring the gap between the wafer and the mask, a method in which a high resolution camera is used to perform image processing, and another method in which a high resolution camera and electrostatic capacitance type sensors are used in combination are known.
However, since the electrostatic capacitance type sensors and the high-resolution camera are both quite expensive, if a gap measurement method employs both the electrostatic capacitance type sensors and the high-resolution camera, the overall apparatus for carrying out such a method will become expensive. In particular, an electrostatic capacitance type sensor capable of measuring a gap of 50 μm or smaller is extremely expensive. Moreover, it will be necessary to use expensive lens to photograph a gap of 20 μm or smaller.
In addition, a high-resolution camera usually requires a large space in order to be installed in an appropriate manner. For this reason, it will be difficult to manufacture a compact exposure apparatus.